A bulk carrier, or bulk material carrier, refers to a variety of devices that permit transport and/or storage of bulk material. Therefore, and by way of example, the term bulk carrier encompasses both stationary and vehicular vessels including tank-type vehicles, such as trucks or truck trailers, railway cars, such as hopper and tank-type cars, barges and the like, and may be used for bulk ladings such as liquids, food grains, and pelletized materials, to name a few. The bulk carrier often is designed to have a closable compartment in which the bulk material is received and stored, the compartment often times being sealed and possibly pressurized.
The bulk carrier typically is designed with a manhole system permitting access to the closable compartment. It should be noted that a variety of structures may be provided for the bulk material to be introduced into and/or removed from the compartment other than a manhole system. However, the manhole system allows a person to physically enter the closable compartment, such as may be required for inspecting or cleaning the compartment interior. The manhole system, nonetheless, allows bulk material to be filled into or drawn out of the compartment.
The common industry practice is for a bulk carrier to be positioned to allow an input or output apparatus to align with the manhole system. The manhole system is opened, most often by a person climbing onto the bulk carrier and manually opening the manhole cover itself by moving it from a closed position over the opening to an open position substantially away from the opening, whereupon the input or output apparatus is positioned proximate to or within the opening for introducing bulk material to, or removing bulk material from, the compartment.
For a number of reasons, it has become desirable to have the opening and closing of the manhole cover be done by remote actuation. This obviates the need for a person to climb onto the bulk carrier, and makes the opening/closing a faster operation. However, these powered systems have brought to light a new set of issues. One such issue is that, without being able to see the manhole system located on a top surface of the bulk carrier, an operator may have difficulty recognizing the exact position of the manhole cover over the opening and cannot inspect the system prior to closing to make sure it is clear of errant bulk material or other debris.
Another issue for these powered systems is the size of the manhole or cover itself. In some manhole designs, the manhole cover shifts in a straight line along a longitudinal direction of the bulk carrier away from the opening. Such a system may utilize a piston for shifting the manhole cover in one direction, which necessitates the piston being at least greater than the size of the manhole cover itself, as well as a rail system for supporting the manhole cover as it moves away from the opening. This leads to a large and possibly expensive system, and the rails may have to be precisely positioned along the top of the bulk carrier which itself may be a rounded tank surface. This makes it difficult to retrofit or install the manhole system on a bulk carrier.
Another manhole system has the cover pivot upwardly. As the manhole cover is relatively large and made of metal, its weight requires a large piston in order to accommodate the large torque required to lift the manhole cover. Furthermore, the manhole cover in an upright position is an obstruction to equipment used for loading and unloading the bulk material from the carrier.
A manhole system shown in U.S. Pat. No. 6,053,348, to Morch, shows a manhole cover that is pivoted around a substantially vertical axis. This system utilizes an actuating mechanism positioned between the axis and opening so that a relatively short piston may be used to shift the manhole cover between open and closed positions. However, the manhole system of the '348 patent still suffers from a number of deficiencies. For instance, an operator of the manhole system of the '348 patent is still unable to determine the exact position of the manhole cover.
Of greater concern is the locking of the manhole cover. It is common for manhole systems to have braces or catches to assist in locking the manhole cover in the closed position. One or more catches are mounted with a stationary portion of the system or with the bulk carrier itself, such as an upstanding annular lip formed on the bulk carrier, and one or more catches are also provided on the manhole cover. When the manhole cover is moved to the closed position, the stationary catches engage with the manhole cover, and the manhole cover catches engage with the stationary portion of the system or the bulk carrier.
In non-powered manhole systems, the operator would manually shift the catches between locked and unlocked positions. With the powered systems, the catches have but a single position. As the catches need to permit the manhole cover to shift between the open and closed positions, their effectiveness in securing with the manhole cover is less than desirable. The use of an inflatable seal between the manhole cover and the opening frame closes any space therebetween, but does not help in locking the hatch because support structures provided for permitting movement by the manhole cover, such as the rails or a pivot pin forming the pivot axis, do not allow any other type of movement of the manhole cover relative to the catches. To the extent such other type of movement occurs, it may have deleterious effects on the support structures, such as bending of the pivot pin.
Accordingly, there has been a need for an improved remotely-actuated manhole system.